Circulating fluid bed reactors have a variety of uses in commercial scale chemical processing. For example, circulating fluid bed reactors are used in catalytic cracking processes.
The design of circulating fluid bed reactors have become of particular importance in fluid catalytic cracking processes with the advent of highly active catalytic cracking catalysts. A concern in designing such reactors is the ability to quickly and effectively separate reacted products from active catalyst within the reaction zone.
U.S. Pat. No. 4,035,284, for example, discloses a circulating fluid bed reactor system having a reaction zone that has a hydrocarbon residence time of 0.5 to 10 seconds. The reaction product is initially separated from the catalyst exiting the reaction zone by contacting plates that extend from the exit of the reaction zone.
U.S. Pat. No. 4,664,888 discloses a circulating fluid bed reactor system having a reaction zone that has a hydrocarbon residence time of 0.2 to 10 seconds. At the exit of the reaction zone is a separation device for separating catalyst from product. The device is semicircular and designed to use centrifugal force to separate the catalyst from the product.
Circulating fluid bed reactors are also likely to be used in the commercial scale operation of converting methanol or dimethyl ether to olefins. Currently, little is known about how to operate these types of reaction systems at commercial scale. However, it is likely that highly active molecular sieve catalysts will be used, and the ability to control such systems will be very important.
In operating highly active catalyst systems, limited ability to control the operation of commercial scale reactor systems is available. Known systems are typically designed to accommodate a certain content of catalyst and a certain throughput of feed. In general, the ability to control the amount of catalyst in the reaction zone is intimately associated with the amount of catalyst that can be circulated through the system, and the amount of feed that can flow through the reactor. In systems that use new and/or highly active catalysts, it would be advantageous to have the ability to independently control such parameters so as to enhance the ability to produce the desired product.